Modern photocopiers, especially color photocopiers, have greatly improved the ability of counterfeiters to accurately copy valuable documents such as checks, notes, bonds, etc.
Over the years various methods have been developed to make such documents resistant to photocopying. Such methods usually revolve either a special ink composition; a particular printed pattern; or minute gradations in the thickness of the printed image, or some combination of these methods, all of which result in making the document either wholly or partially resistant to photocopying.
Gardner et al. (U.S. Pat. No. 4,522,429) teaches the use of a combination of known specific colors of ink to achieve a printed image which has a reflection spectral response of less than about 10% for light with a wavelength below about 600-650 millimicrons. Thus the printed image is within the visible range of the eye but cannot be photocopied because it does not reflect in the range of light used in a photocopier, which is below about 600-610 millimicrons. This invention has the disadvantage of having a very narrow window where the pigment is both reflective and visible to the eye. Therefore, the printed matter on the document is quite light, making this technique impracticable for use with face-value documents such as checks, notes, bonds, etc.
La Capria (U.S. Pat. No. 4,066,280) teaches imprinting a document with two kinds of ink which overlap each other on the document. Most of the document is imprinted with conventional ink which is light absorptive. Overlapping or being overlapped by this conventional ink is a second imprint on the document which is of a specularly reflective coloring ink containing aluminum powder. This second imprint is a multiplicity of dots or lines which are difficult to reproduce by hand. This invention has several disadvantages, mostly as a result of the presence of the aluminum powder. No matter how fine the aluminum powder is it tends to accumulate in the fountains of printing presses. Furthermore, the reflective qualities of the aluminum powder can be significantly diminished as the document becomes soiled through normal usage. Furthermore, since the portion of the document printed with the reflective ink has a special pattern, it requires redesigning documents to incorporate such a special pattern.
Wicker (U.S. Pat. No. 5,271,645) teaches imprinting documents with ink which is a mixture of conventional ink material (pigments, dyes, etc.) as well as fluorescence compounds which are at a certain threshold level so that when the mixture is exposed to ultraviolet light the fluorescence is barely discernible to the eye. When a document imprinted with such a mixture is color photocopied, there is a significant diminution of color and overall quality. This invention has the disadvantage of requiting a very specific mixture of ink which has the potential to be difficult to replicate consistently in order to achieve the desired photocopy-resistant qualities.
Castagnoli (U.S. Pat. No. 4,588,212) teaches the imprinting of a safety design on a valuable document such as a bank note. This design is achieved by having juxtaposed groups of segments of parallel raised lines having two different heights, forming high and low reliefs, extending by turns in two predetermined different directions whereby the segments of one group are not parallel to those of an adjacent group. A first transitory image is formed by the high raised segments parallel to the first direction. A second transitory image is formed by the high raised segments parallel to the second direction. Such images cannot be photographed or photocopied but can only be visualized by the eye when the printed image is viewed from a certain angle. This invention has the disadvantage of being expensive to produce. Furthermore, it is only appropriate for documents which use very concentrated, ornate printing indicia, such as intaglio printing used with paper money. It is therefore not practical to use it for bank checks and other documents which need to be produced more inexpensively with less dense printing on the document.
Burnham et al. (U.S. Pat. No. 4,884,828) teaches an improvement on the moire pattern conventionally used to provide security against counterfeiting in valuable documents. The moire pattern generally uses interference fringes arising from two sets of generally parallel lines. The line sets are superimposed upon one another with their lines intersecting and mutually inclined at a small angle. With the use of high quality photocopiers, especially color copiers, the moire pattern is no longer an effective anti-counterfeiting device. Bunham's improvement relates to a pattern formed of first and second sets of intersecting lines arranged to form one or more moire effect interference fringes by having at least one of the line sets vary progressively in both line thickness and line spacing along their length. The photocopy-resistant function of this invention is improved when each line set is printed in a different color of ink. As a further improvement to the invention, the inks used can be inks which are known to have other anti-fraud characteristics such as solvent-sensitive inks, water-fugitive inks or UV-fluorescent inks which are invisible in daylight or normal artificial light. The disadvantages of the Bunham method are similar to the disadvantages with Castagnoli as well as LaCapria. First of all, moire patterns are best used in documents, such as bank notes which are printed with very dense indicia. They are not practical for use with bank checks. Furthermore, the use of this pattern involves redesigning the document to incorporate the moire patterns necessary to produce the photocopy-resistant effect.
Caprio et al. (U.S. Pat. No. 4,582,346) teaches a document substrate with background printed matter on a first portion of the surface of the substrate and a warning printed matter on a second portion of the surface of the substrate. The warning printed matter is not easily visible to the eye but when the document is photocopied, the warning printed matter is easily visible because of photocopier directional slur. This invention has many of the same disadvantages discussed above. It necessarily involves a densely concentrated printed indicia on the document in order to be able to produce the necessary effect of being invisible on the original document and visible in a photocopy. This also involves the necessity of redesigning any previously used documents in order to be able to incorporate the warning printed matter into the document
Wicker (U.S. Pat. Nos. 5,018,767 and 5,193,853) teaches an invention in which documents are imprinted with lines formed into various patterns imitative of intaglio or gravure printing. The pitch of the lines is deliberately selected so as to vary minutely from the pitch of the scanning trace of various copying machines. The variation in pitch may be obtained by deliberately manufacturing the document with the desired pitch or, subsequent to the image placement therein, altering the dimensions or geometry of the document so as to effectively skew the pitch parameter, by heating the printing matte to subtly alter the imprinted pattern. As with several of the other inventions discussed above, because this method involves specifically designing an imprinted indicia on a document to have a desired pitch, this method necessarily involves redesigning a previously used document. Furthermore, because this method requires the use of intricate patterns, such as patterns which imitate the gravure or intaglio printing methods, it is somewhat restricted in the type of printed indicia which can be used. It is also likely that an imprinted pattern which is photocopy resistant on one type of photocopier will not be photocopy resistant on another type of photocopier.
The present invention overcomes the problems and disadvantages of the above-discussed patents. It does not involve the necessity of using intricate styles of printing and thus can be adapted to be used with preexisting printing designs. The ink used in printing the photocopy-resistant indicia of the present invention is easy to produce and obtain and is identifiable by specific colors specifically identified by the trademark "Pantone Matching System" numbers. (Pantone Matching System is a trademark of Pantone, Inc.) It does not involve the use of metallic powders or other additives in the ink which have a tendency to accumulate in printing fonts. Nor does it rely on specular qualities in the ink which have a tendency to be diminished over time as the document becomes soiled and faded.